In recent years, with the progress of society, the research and manufacture of display devices have entered the center of human social and cultural activities, and have made brilliant achievements in technology and commerce. With the shrinking market of cathode-ray tubes (CRTs), various flat panel display technologies compete with each other and are widely used in various communication devices such as televisions, mobile phones and computers, and then the flat panel display industry rises rapidly. Thin film transistors are core components in the flat panel display technology. As switch control elements or integrated components of peripheral driver circuits, performance of the thin film transistors directly affects the effect of flat panel displays.